This invention relates to a shutter control in the flash photographing mode of a camera equipped with an electronic shutter and capable of automatic exposure control and a flash light control circuit.
In photographing with a camera equipped with an automatic control type flash device (the so-called autostrobo), it is not necessary to provide any distance factor for the automatic control type flash device. The automatic control type flash device interrupts the duration of flashing when an appropriate flash quantity is detected by receiving the reflection of the flash on a photographing object by a photoelectric element provided for the flash device. Accordingly, it is necessary to provide a photoelectric element of a superior responsiveness for the flash device, while it is customary to provide a photoelectric element for the camera for automatic exposure control. Accordingly, it is advantageous to provide a photoelectric element of a superior responsiveness for the camera and make the photoelectric element serve also as the photoelectric element of the flash device. Such a system has already been employed by some cameras.
In the shutter control circuit of the present invention, a photoelectric element of a camera is adapted to serve both for controlling the shutter operation and for controlling the flash device. This invention relates particularly to a shutter control circuit suitable for daylight flash photographing (designated as "daylight synchro-flash photographing" hereinafter).
The exposure of the conventional camera in synchro-flash photographing has been controlled by integrating the sum of the quantity of the natural or ambient light (daylight) received from the object field and the quantity of the flash light received from the object field, and then simultaneously interrupting the flashing and providing a signal to close the shutter when the integrated quantity of the daylight and the flash light reach a predetermined given value. Accordingly, it has been necessary to actuate the flash trigger switch in synchronism with the start of exposure operation of the shutter, the adjustment of which has been very difficult. The application of an exposure control system such as described hereinbefore, in which the quantity of the daylight and the quantity of the flash light are integrated simultaneously, to a program lens shutter which opens in a controlled speed is accompanied by problems that the shutter does not open due to the excessively intensive reflection of the flash when the object is located very near to the camera and that the efficiency of the flash is reduced resulting from the arrival of the peak flash timing before the shutter full opening timing when the object is located far from the camera.